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Re: What executes faster?

From: "Reinoud van Leeuwen" <reinoud(at)xs4all(dot)nl>
To: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: What executes faster?
Date: 2001-10-01 09:39:45
Message-ID: 24970.194.109.0.126.1001929185.squirrel@webmail.xs4all.nl (view raw or flat)
Thread:
Lists: pgsql-hackers
> [HACKERS] What executes faster? 
> Now that I've found the solution for my duplicate key problem, 
> I'm wondering what executes faster when I have to check for 
> duplicates. 
> 1. try to update 
>    if no row affected -> do the insert 
>    else done 
> 2. do a select 
>    if row not found -> do the insert 
>    else do the update 
> Another idea I'm thinking about: 
> I'm doing the check for duplicate key by myself now. 
> Aren't insert commands running faster, if I replace 
> an unique index by a not-unique index. 

I have solved an almost similar problem.
I have a large table (about 8 milion rows) called radius and a table with 
updates and newlines called radiusupdate.
The first thing I tried was 2 queries:
update radius 
  from radiusupdate 
 where radius.pk = radiusupdate.pk

insert into radius 
select * 
  from radiusupdate RU
 where RU.pk not in (select pk from radius)

But the second one is obviously not very fast. A "not in" never is... So I 
now do things just a little bit different. I added a field to the table 
radiusupdate called "newline". It is default set to true. Then I replace 
the second query by these two:

update radiusupdate
   set newline = false
  from radius R
 where radiusupdate.pk = radius.pk

insert into radius
select *
  from radiusupdate RU
 where newline = true

This is a lot faster in my case....

Reinoud


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